docs: add redpanda_trust_file_crc32c and redpanda_truststore_expires_at_timestamp_seconds metrics (#1236)

Author: paulohtb6

modules/reference/pages/public-metrics-reference.adoc

@@ -1859,6 +1859,34 @@ Indicator of whether a resource has at least one valid TLS certificate installed
 
 ---
 
+=== redpanda_trust_file_crc32c
+
+CRC32C checksum calculated from the contents of the trust file. This value is calculated when a valid certificate is loaded and a trust store is present. Otherwise, the value is zero.
+
+*Type*: gauge
+
+*Labels*:
+
+- `area`
+- `detail`
+- `shard`
+
+---
+
+=== redpanda_truststore_expires_at_timestamp_seconds
+
+Expiry time of the shortest-lived CA in the truststore, measured in seconds since epoch.
+
+*Type*: gauge
+
+*Labels*:
+
+- `area`
+- `detail`
+- `shard`
+
+---
+
 [[data_transform_metrics]]
 == Data transforms metrics